1. Field of the Invention
The present invention relates to a video display processor for use in terminal equipment for a computer, a game machine or the like.
2. Prior Art
There have been proposed various kinds of display control systems which comprise a video display processor and display animation and still images on a screen of a CRT (cathode-ray tube) display unit under the control of a CPU (central processing unit). FIG. 1 shows one example of such conventional systems which comprises a video display processor (hereinafter referred to as "VDP") 101 and a central processing unit (CPU) 102. The system further comprises a memory 103 which includes a ROM (read only memory) storing a variety of programs to be executed by the CPU 102 and a RAM (random access memory) for storing other necessary data. The CPU 102 outputs data representative of still and animation images to be displayed on a screen of a CRT display unit 104 to the VDP 101 which in turn stores the still and animation data into a video RAM (hereinafter referred to as "VRAM") 105.
Upon receipt of a display command from the CPU 102, the VDP 101 sequentially reads the still and animation data from the VRAM 105 in accordance with scanning synchronization signals of the CRT display unit 104, and supplies the read data to the CRT display unit 104 thereby to display the still and animation images on the screen of the CRT display unit 104.
In such a video display control system, it is frequently desired to use an input control device such as a mouse or a light pen to facilitate the input of X-Y coordinates of a selected display point in a video image on the screen so that the system can be used for various purposes. However, what has not heretofore been proposed is a video display processor which is connectable to such an input control device and capable of processing the point on the screen by it in the form of X-Y coordinates. Incidentally, when a video display processor is used with an input control device such as a light pen, the processor should generate data representative of X-Y coordinates of a display point on the screen which is selected through the light pen. On the other hand, when the video display processor is used with an input control device such as a mouse, the processor should generate data representative of the amount of movement of the mouse. Therefore, a video display processor which is connectable to both of a light pen and a mouse should incorporate therein a complicated circuitry including at least two different data generating circuits. However, in order to construct such a video display processor as an LSI chip, the circuitry should be minimum.